Connect Bluetooth Mouse at Boot Time

Add device to hcid.conf
Edit "/etc/bluetooth/hcid.conf". Add following lines:

device <Bluetooth Address> {
name "<Device Name>"
}

Your can get the bluetooth address and device name by "hcitool scan"

Pair device
hidd --search

Connect at boot time
Edit "/etc/default/bluetooth". Change

HIDD_ENABLED=0

to

HIDD_ENABLED=1


All set! Restart your computer.

Reference:
HOWTO: Logitech Bluetooth Mouse & Keyboard